Pressure Control Devices for Sealing Around Tubular Members

ABSTRACT

A pressure control device for sealing about a tubular string comprises: a flange disposed about a central axis, an annular extension extending from the flange and an annular seal element coupled to the annular extension. The seal member includes a through-passage for receiving the tubular string and an annular recess in which the annular extension is disposed. The annular extension includes a radially-inward facing surface that includes a tapered region that is nonlinear in an axial cross-section for reducing mechanical stresses in the seal member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional application Ser. No. 62/622,428 filed Jan. 26, 2018, and entitled “Pressure Control Devices for Sealing Around Tubular Members,” which is hereby incorporated herein by reference in its entirety for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND Field of the Disclosure

The present disclosure relates generally to drilling systems and to rotating control devices (RCD) for such systems. More particularly, the disclosure relates to systems and methods for providing annular seals between concentric fluid conduits as they rotate relative to each other and as one of the fluid conduits moves axially through the RCD.

Background to the Disclosure

In applications requiring the transmission of fluid under relatively high pressure, it is sometimes necessary to interconnect a rotatable conduit with a stationary conduit, and to provide seals therebetween to prevent leakage of the pressurized fluid. One such application is in drilling operations where a drill pipe or another tubular member passes through a rotating control device (RCD), where the outer housing of the RCD remains stationary while an internal sleeve and packing elements, which are seals, surround and rotate along with the drill pipe. In this arrangement the sleeve and the drill pipe are rotatable conduits. Each packing element includes a rigid annular insert having a mounting flange and a resilient annular seal element that surrounds and contacts the pipe. The packing elements allow the drill pipe to move axially into or out from a wellbore without fluid leakage.

During operation, axial movement of the drill pipe through the RCD causes the resilient the seal elements to deform, expanding and contracting in response to varying outside diameter of the drill pipe and its joints. Such deformation induces life-reducing and thus undesirable mechanical stress in the seal elements.

FIG. 1 shows a finite element analysis (FEA) plot of stress induced within a resilient, annular seal element PA2 of a conventional packing element. The plot shows stress results for regions along a cross-section; even so, the results are representative of volumetric portions of the seal element. Seal element PA2 extends from a first end PA4 to a second end PA6 and includes a through-passage PA8, an annular recess PA10 extending inward from first end PA4, and a radially outermost surface PA12. Although not shown, the FEA included boundary conditions that assume a rigid flanged, annular insert of the packing element is located along the radially outer portion of first end PA4 and within annular recess PA10. Annular recess PA10 is generally cylindrical, having axially extending walls. In the plot, a box end 20 of a drill pipe 22 is located within a seal element PA2 with neck 24 of box end 20 axially aligned with the innermost end of recess PA10, adjacent the indentation PA11. More specifically, the plot represents a situation in which drill pipe 22 is being pulled upward through seal element PA2. In the plot, stress levels are normalized to values from 0 to 1 in multiple increments, as show on legend 30. For the sake of discussion, three stress levels SL1, SL2, SL3 will be considered, with each stress level representing one or more increments in legend 30. In this scenario, a region of low stress SL1 in seal element PA2 occurs throughout a majority of seal element PA2, extending axially inward from ends PA4, PA6 and along the outermost surface PA12 and the lower and upper portions of through-passage 266. A region of elevated stress SL2 occurs adjacent neck 24, adjacent recess PA10, and below recess PA10. A region of highest stress SL3 extends radially between neck 24 and the innermost end of recess PA10, spanning the entire radial distance therebetween.

When it is believed that a seal failure may have occurred, drilling operations are typically halted so that the seals can be inspected and possibly replaced. However, drilling costs are very high, such that downtime must be avoided or minimized as much as possible. Consequently, systems and apparatus that extend the life of the packing elements would be welcomed by the industry.

BRIEF SUMMARY OF THE DISCLOSURE

These and other needs in the art are addressed by a pressure control device having components configured to work together to minimize damaging mechanical stresses and thereby to extend the life of seals and decrease the likelihood that drilling operations must be shut down in order to replace seals. In one embodiment, a pressure control device for sealing about a tubular string comprises: a flange disposed about a central axis, an annular extension extending from the flange and having a radially-inward facing surface; and an annular seal element coupled to the annular extension. The seal member includes a through-passage for receiving the tubular string and an annular recess in which the annular extension is disposed. The radially-inward facing surface comprises a tapered region that is nonlinear in an axial cross-section.

In some embodiments, the radially-inward facing surface flares outwardly, away from the through-passage. The radially-inward facing surface may, in some embodiments, include first and second ends wherein the second end is further from the central axis than the first end. In some embodiments, the radially-inward facing surface comprises a first region extending from the first end and a second region extending from the first region, and wherein the second region is continuously curved in an axial cross-section. The second region may include a constant radius in an axial cross-section. Further, in some embodiments, the radially-inward facing surface comprises a first region extending from the first end and a second region extending from the first region, and wherein the second region, in an axial cross-section, has a radius that has a value selected from the range 0 to 30 inches.

In some embodiments the annular seal element comprises: a seal first end adjacent the flange; a seal second end axially spaced apart from the flange; and a radially outermost surface having first and second regions, wherein the first region extends from the seal first end and the second region extends from the seal second end toward the seal first end and is frustoconical.

Also disclosed herein is a pressure control device for sealing about a tubular string, comprising: a central axis; an annular insert; and an annular seal element coupled to the annular insert. The seal element comprises: a seal first end disposed adjacent the annular insert; a seal second end axially spaced apart from the annular insert; a through-passage extending through the seal first and second ends for receiving the tubular string; and a radially outermost surface including a first region extending from the seal first end and a second region extending from the seal second end toward the first region, wherein the second region tapers as it extends in a direction away from the annular insert. In some embodiments, the second region on the annular seal element intersects the first region, and in some embodiments, the second region is frustoconical. In some embodiments, the annular insert comprises an annular flange disposed about the central axis; an annular extension extending from the flange; and a radially-inward facing surface extending along the annular extension, wherein the annular seal element includes an annular recess in which the annular extension is disposed, the annular recess extending from the seal first end. The radially-inward facing surface of the annular insert includes a tapered region that expands radially outwardly as it extends axially away from the flange. The radially-inward facing surface may, in some embodiments, further include a generally cylindrical region extending from the flange to the tapered region.

Another pressure control device for sealing about a tubular string is disclosed and comprises: a central axis; an annular insert, and an annular seal element. The insert includes a flange disposed about the central axis, an annular extension concentric with the flange and extending from the flange, and a radially-inward facing surface extending along the annular extension. The annular seal element is coupled to the annular extension. The seal element includes: a seal first end disposed adjacent the flange; a seal second end axially spaced apart from the flange; a through-passage extending through the seal first and second ends for receiving the tubular string; and an annular recess in which the annular extension is disposed. The seal element further includes a radially outermost surface having a first region extending from the seal first end and a second region extending from the seal second end toward the first region. The radially-inward facing surface of the annular insert includes a tapered region that expands radially outwardly as it extends axially away from the flange.

In some embodiments, the second region on the annular seal element intersects the first region and in some embodiments, the tapered region is continuously curved. The tapered region of the annular insert may have a constant radius as viewed in a profile on an axial plane.

In some embodiments, the radially-inward facing surface of the annular insert comprises: a first end coupled to the flange, a second end spaced from the first end; and a cylindrical region extending from the first end; wherein the tapered region extends from the cylindrical region toward the second end. In some embodiments, the tapered region of the radially-inward facing surface intersects the second end at a fillet; and wherein the tapered region intersects the fillet at a tangent line that is disposed at angle between 5 and 45 degrees, inclusive, with respect to the central axis.

Thus, embodiments described herein include a combination of features and characteristics intended to address various shortcomings associated with certain prior devices, systems, and methods. The various features and characteristics described above, as well as others, will be readily apparent to those of ordinary skill in the art upon reading the following detailed description, and by referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the disclosed exemplary embodiments, reference will now be made to the accompanying drawings:

FIG. 1 shows a finite element analysis plot of stress induced within a conventional packing element;

FIG. 2 shows cross-sectional side view of an embodiment of a rotating control device having a pressure-responsive assembly mounted in a rotating sleeve in accordance with principles described herein;

FIG. 3 shows a perspective view of an embodiment of a packing element configured for use in compatible with the rotating control device of Figure, the packing element having an annular insert and an annular seal element in accordance with principles described herein 1;

FIG. 4 shows a cross-sectional view of the packing element of FIG. 3;

FIG. 5 shows a cross-sectional view of the annular insert of the packing element of FIG. 4;

FIG. 6 shows a cross-sectional view of another embodiment of a packing element configured for use in compatible with the rotating control device of FIG. 2 in accordance with principles described herein;

FIG. 7 shows a cross-sectional view of still another embodiment of a packing element configured for use and compatible with the rotating control device of FIG. 2 in accordance with principles described herein;

FIG. 8 shows a finite element analysis plot of an example stress-loading within the packing element of FIG. 6; and

FIG. 9 shows a finite element analysis plot of an example stress-loading within the packing element of FIG. 4.

NOTATION AND NOMENCLATURE

The following description is exemplary of certain embodiments of the disclosure. One of ordinary skill in the art will understand that the following description has broad application, and the discussion of any embodiment is meant to be exemplary of that embodiment, and is not intended to suggest in any way that the scope of the disclosure, including the claims, is limited to that embodiment.

The figures are not drawn to-scale. Certain features and components disclosed herein may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness. In some of the figures, in order to improve clarity and conciseness, one or more components or aspects of a component may be omitted or may not have reference numerals identifying the features or components. In addition, within the specification, including the drawings, like or identical reference numerals may be used to identify common or similar elements.

As used herein, including in the claims, the terms “including” and “comprising,” as well as derivations of these, are used in an open-ended fashion, and thus are to be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” means either an indirect or direct connection. Thus, if a first component couples or is coupled to a second component, the connection between the components may be through a direct engagement of the two components, or through an indirect connection that is accomplished via other intermediate components, devices and/or connections. The recitation “based on” means “based at least in part on.” Therefore, if X is based on Y, then X may be based on Y and on any number of other factors. The word “or” is used in an inclusive manner. For example, “A or B” means any of the following: “A” alone, “B” alone, or both “A” and “B.”

In addition, the terms “axial” and “axially” generally mean along or parallel to a given axis, while the terms “radial” and “radially” generally mean perpendicular to the axis. For instance, an axial distance refers to a distance measured along or parallel to a given axis, and a radial distance means a distance measured perpendicular to the axis. Furthermore, any reference to a relative direction or relative position is made for purpose of clarity, with examples including “top,” “bottom,” “up,” “upper,” “upward,” “down,” “lower,” “clockwise,” “left,” “leftward,” “right,” and “right-hand.” For example, a relative direction or a relative position of an object or feature may pertain to the orientation as shown in a figure or as described. If the object or feature were viewed from another orientation or were implemented in another orientation, it may then be helpful to describe the direction or position using an alternate term.

DETAILED DESCRIPTION OF THE DISCLOSED EXEMPLARY EMBODIMENTS

The present disclosure involves sealing between a rotatable conduit and a stationary conduit to prevent fluid leakage. The sealing is achieved by a packing element(s), which serves as a pressure control device and may rotate with the rotatable conduit or may remain stationary with the stationary conduit. Each packing element includes an annular insert having a mounting flange and an annular seal element that surrounds and contacts the pipe. Axial movement of a drill pipe or another tubular string through the packing element may cause the annular seal element, which includes a resilient portion, to deform as it expands and contracts in response to varying outside diameter of the tubular string and its joints. Deformation causes stress in the resilient portion. The packing element embodiments disclosed herein are configured to reduce stress within the seal element as a drill pipe or another tubular string slides into or through the packing element or remains sealingly coupled within the packing element.

Referring to FIG. 2, in an exemplary embodiment, a rotating control device (RCD) 100 extends along a central axis 101 and is configured to receive sealingly a tubular member, which in this example is a pipe 102. Device 100 is suitable as a member of a wellhead over a borehole of a well, such as a hydrocarbon well, for controlling or isolating fluid pressures. As such, RCD 100 is a type of pressure control device. Device 100 includes an outer housing 110 holding a sensor 120 and includes a rotating sleeve assembly (RSA) 125 received within housing 110.

Housing 110 includes a housing wall or tubular body 111 extending along the central axis 101 from a lower end 112 to an upper end 113, having an outer surface and a through-bore 114. Through-bore 114 is centered on axis 101 and defines an inner wall.

RSA 125 extends at least partially within the through-bore 114 of housing 110. RSA 125 includes a rotatable sleeve 130 received within a bearing assembly 180 to rotate about axis 101 relative to the housing 110, a speed indicator 131 received in sleeve 130 at a location along axis 101 that is aligned with sensor 120 of outer housing 110. Sleeve 130 and pipe 102, when installed, are configured as a rotatable conduit, and housing 110 is configured as a stationary conduit. Sensor 120 is configured to detect the periodic presence of speed indicator 131 as sleeve assembly 125 rotates relative to housing 110 and sensor 120.

In FIG. 2, speed indicator 131 includes a magnet, and sensor 120 is includes Hall Effect sensor; although, various other embodiments include another type of speed indicator 131or another type of sensor 120.

Rotating sleeve 130 includes a sleeve outer surface 134 and a bore 136 extending from a lower end 132 to an upper end 133. In FIG. 2, rotating sleeve 130 is formed from an upper sleeve member 140 coupled to a lower sleeve member 160 by a sleeve coupling 165. Referring to FIG. 2, a collar 168 is coupled to sleeve member 140 at upper end 133, and an upper packing element 170A extends downward from the bottom of collar 168, into member 140. Collar 168 is generally tubular, being open at both ends to receive pipe 102 therethrough. A lower packing element 170B extends downward from sleeve member 160 at lower end 132. Each packing element 170A,B includes annular insert 172 bonded or otherwise coupled to an annular seal element 174 extending axially from insert 172. Annular inserts 172 are fastened to collar 168 and sleeve member 160, respectively. The annular seal element 174 of packing element 170A,B are configured to seal around the circumference of pipe 102, isolating the bore 136 from an upper portion of collar 168 and from upper and lower portions of bore 114 in housing 110, to prevent fluid leakage from these regions. Thus, these and other packing elements disclosed herein are pressure control devices. The sealing configuration of packing elements 170A,B is maintained even as sleeve 130 and pipe 102 rotate relative to housing 110 during operation. In at least some modes of operation, rotation of pipe 102 causes sleeve 130 to rotate due to the gripping action of packing elements 170A,B. Collar 168, packing elements 170A,B, and bore 136 provide a sealable through-passage for a tubular member, e.g. pipe 102, to extend or pass through housing 110, which in some arrangements leads into a borehole. Bore 136 is configured to be an isolated chamber when a tubular member is installed.

Upper sleeve member 140 includes a threaded lower end 142 attached to sleeve coupling 165 and an upper end 133 attached to collar 168. Sleeve member 140 includes a radially protruding annular shoulder 146 located between ends 142, 133 and a port 148 extending into shoulder 146 along a central axis 149 coplanar with central axis 117 of port 116. Some misalignment between axis 149 and 117 is acceptable in various embodiments depending on the sensitivity of sensor 120. Port 148 is configured to receive speed indicator 131 at a fixed position along port axis 149, disposing speed indicator 131 at a fixed distance from axis 101, being generally flush or adjacent to outer surface 134. Whenever sleeve 130 rotates the indicator 131 to the circumferential position of sensor 120, the magnet of indicator 131 is at a fixed distance from sensor 120 within its detection range (e.g. a prescribed distance). Repeated movement of speed indicator 131 past sensor 120 provides a measurement of the rotational speed of sleeve 430 with respect to housing 110. Thus sensor 120 is configured as a speed sensor.

Referring again to FIG. 2, bearing assembly 180 includes a bearing housing 182 that is coupled within housing 110 to remain stationary, a bearing sleeve 184 coupled to sleeve 130 to grasp and rotate with sleeve 130, and bearing 186 coupled between housing 182 and sleeve 186. In this example, bearing 186 includes two opposing sets of tapered roller bearings to resist axial thrust in either vertical direction from, for example, pipe 102.

FIG. 3 presents a packing element 200. One or more packing element 200 may be installed or used as either or both packing elements 170A, 170B in RSA 125 of FIG. 2 to perform as a pressure control device for sealing about a tubular string. Packing element 200 includes an axis 202, an annular insert 204 centered on axis 202, and an annular, resilient seal element 205 extending from insert 204 and centered on axis 202. Annular insert 204 includes a flange 206 with a plurality of fastener holes 208. Seal element 205 includes a radially outermost surface 212 having a plurality of axial slots 214. Each slot 214 is circumferentially aligned with an axially extending, fastener hole 208 in flange 206 to allow a fastener to extend therein.

FIG. 4 shows a cross-sectional view of packing element 200, the cross-sectional view formed along a geometric plane 215 that intersects central axis 202. Insert 204 includes a first end 222, a second end 224 spaced apart from first end 222 along axis 202, a flange 206 disposed about axis 202 at end 222, an annular extension 226 concentric with flange 206 extending from the flange 206 to end 224, and a radially-inward facing surface 230 extending along flange 206 and annular extension 226. In this example, and as shown in profile view in FIGS. 4 and 5, surface 230 is nonlinear along axial plane 215.

FIG. 5 shows a closer view of insert 204 from FIG. 4. From end 222 to end 224, insert 204 has a height 232. Extension 226 has an outside diameter (OD) 233 at least at second end 224 and has an inside diameter (ID) 234 at first end 222. At first end 222, inward-facing surface 230, starting with the ID 234, extends from flange 206. Surface 230 expands and has an inner diameter at second end 224 that is greater than ID 234 at first end 222. Consequently, surface 230 is further from central axis 202 at second at end 224 than it is at the first end 222. Radially-inward facing surface 230 comprises a cylindrical region 236 (i.e. flat along plane 215, i.e. when viewed in the cross-section) extending from the first end 222 and a tapered region 238 extending from the region 236, starting at an axial distance 245 from end 222. Region 238 tapers radially outward from axis 202 as surface 230 extends away from the flange 206. In various embodiments including that of FIG. 4, distance 245 is selected from the range 0 to 90% of height 232. Embodiments having a distance 245 equal to 0 inches lack a cylindrical region 236.

Continuing to reference FIG. 5, tapered region 238 is continuously curved in this embodiment, lacking any radially inward annular protrusion. Tapered region 238 intersects or joins the second end 224 at a fillet 242. In this example, with tapered region 238 shown in profile view, region 238 has a constant radius 244 on axial plane 215. In various embodiments including FIG. 5, radius 244 has a value selected from the range ⅛ inch to ten times OD 233. In various embodiments, including FIG. 5, radius 244 has a value selected from the range ⅛ to 30 inches. In some embodiments, radius 244 has a value selected from outside these ranges. In some embodiments, tapered region 238 has a varying radius along plane 215. In some embodiments, tapered region 238 is flat rather than curved.

Considering surface 230 in FIG. 5 further, tapered region 238 intersects the fillet 242 at a tangent line 246. In various embodiments including FIG. 5, tangent line 246 is disposed at angle 247 having a value between 5 and 45 degrees, inclusive, with respect to central axis 202 on plane 215. In three dimensions, tangent line 246 extends circumferentially as a conical surface about axis 202.

Referring again to FIG. 4, annular seal element 205, includes a seal first end 262 coupled to annular extension 226 and disposed adjacent flange 206 and includes a seal second end 264 axially spaced apart from flange 206. Seal element 205 further includes a through-passage 266 extending through the seal first and second ends 262, 264, an annular recess 268 extending from seal first end 262, and radially outer or outermost surface 212, which extends from first end 262 to second end 264. Through-passage 266 is configured to receive a tubular member or string. Annular extension 226 of insert 204 is disposed and held in annular recess 268. The resiliency of seal element 205 allows a portion of element 205 to expand and contract in response to varying outside diameter or alignment of a tubular string and its joints that may move within the through-passage 266.

Outermost surface 212 includes a first region 272 extending axially from the seal first end 262 at a taper angle 273 with respect to axis 202 and a second region 274 extending from the seal second end 264 toward the first region 272. In FIG. 4, slots 214 extend primarily through region 272 but also region 274. Region 274 becomes smaller as it extends in an axial direction from region 274 toward end 264. Conversely, region 274 becomes larger as it extends in an axial direction from end 264 toward region 274 and annular insert 204. In FIG. 4, the second region 274 is frustoconical, extending at a taper angle 275 with respect to axis 202. Region 274 intersects the first region 272 at a fillet and intersects seal second end 264 at a fillet 276. Thus, in this example, outermost surface 212 includes two regions defined by their axially-extending character, i.e. regions 272, 274 located between ends 262, 264, but not a third region; wherein the fillets are considered to be portions of these regions 272, 274 and not regions in their own right. Region 274 extends from region 272 to end 264 without an intervening cylindrical region. In FIG. 4, taper angle 273 is equal to 2 degrees; thus, the outer extent of region 272 (radially beyond slots 214) is mildly frustoconical. Some embodiments have a greater or lesser value for taper angle 273, and in some embodiments, taper angle 273 may be zero degrees such that the outer extent of region 272 is generally cylindrical. The size of the other taper angle, taper angle 275, may also vary. In various embodiments including FIG. 4, taper angle 275 is selected from a value between 5 and 85 degrees, inclusive. More specifically, in FIG. 4, taper angle 275 is 20 degrees. Axial slot 214 extends from first seal end, along the first region 272, and into the second region 274 of surface 212. For packing element 200, the radially-inward facing surface 230 of insert 204 expands or flares outwardly, away from the through-passage 266 as surface 230 extends axially from flange 206. Packing element 200 has a total height 280 from end 222 to end 264. In various embodiments including FIG. 4, the height 282 of second region 274 of seal element 205, measured from end 264, is selected from a value in the range 10% to 75% of height 280, inclusive. In some embodiments, second region 274 is curved along axis 202 rather than being frustoconical and straight along axis 202 on plane 215.

FIG. 6, in another embodiment, shows a cross-sectional view of packing element 300. One or more packing element 300 may be installed or used as either or both packing elements 170A, 170B in RSA 125 of FIG. 2 to perform as a pressure control device for sealing about a tubular string. Packing element 300 includes an axis 302 located on a geometric plane 303, an annular insert 204 centered on axis 302, and an annular seal element 305 extending from insert 204 and centered on axis 302. Annular insert 204 is the same as previously described with respect to FIGS. 3 and 4, including a radially-inward facing surface 230 extending along a flange 206 and an annular extension 226 from a first end 222 to a second end 224. As shown in the profile view of FIG. 6, surface 230 is nonlinear along axial plane 215.

Annular seal element 305 extends from a seal first end 362 coupled to annular extension 226, adjacent flange 206 to a seal second end 364 axially spaced apart from flange 206. Seal element 305 further includes a through-passage 266 extending through the seal first and second ends 362, 364, an annular recess 268 extending from seal first end 362, and a radially outermost surface 312 extending from first end 362 to second end 364, and having a plurality of axial slots 214, in surface 312. Each axial slot 214 is aligned with a fastener hole 208 in flange 206. Only one pair of aligned slot 214 and hole 208 is shown in FIG. 6. Through-passage 266 is configured to receive a tubular member or string. Annular extension 226 of insert 204 is disposed and held in annular recess 268. Seal element 305 includes flexible or resilient material to expand and contract in response to varying outside diameter or alignment of a tubular string and its joints that may move within the through-passage 266.

Outermost surface 312 includes a first region 372 extending from the seal first end 362 at a mild taper with respect to axis 302, a tapered second region 374 extending from the first region 372, and a cylindrical, third region 376 extending from the second region 374 to the seal second end 364. Second region 374 and third region 376 intersect at an obtuse angle 377. In FIG. 6, second region 374 is frustoconical, having taper angle 375 that is substantially greater than the taper of region 372, and the cylindrical, third region 376 intersects seal second end 364 at a fillet 378. Taper angle 375 of second surface region 374 is 30 degrees, but angle 375 could vary in other embodiments. For example, angle 375 may have a value between 5 and 85 degrees. In some embodiments, third region 376 is mildly tapered, frustoconical with respect to central axis 302. For packing element 300, the radially-inward facing surface 230 of insert 204 expands or flares outwardly, away from the through-passage 266 as surface 230 extends axially away from flange 206.

FIG. 7 shows a cross-sectional view of in another embodiment, a packing element 400. One or more packing element 400 may be installed or used as either or both packing elements 170A, 170B in RSA 125 of FIG. 2 to perform as a pressure control device for sealing about a tubular string. Packing element 400 includes an axis 402 located on a geometric plane 403, an annular insert 404 centered on axis 402, and an annular seal element 205 extending from insert 404 and centered on axis 402.

Annular insert 404 includes a first end 422, a second end 424 spaced apart from first end 422 along axis 402, a flange 206 disposed about axis 402 at end 422, an annular extension 426 concentric with flange 206 extending from the flange 206 to end 424, and a cylindrical radially-inward facing surface 430 extending along flange 206 and annular extension 426, and a plurality of axially extending fastener holes 208. The profile view of FIG. 7 shows that surface 430 is linear along axial plane 215 and includes an annular protrusion 431 proximal end 424. Protrusion 431 may aid in keeping seal element 205 coupled to insert 404.

Annular seal element 205 is the same as previously described with respect to FIG. 3, including the possible embodiments thereof. For example, seal element 205 extends from a seal first end 262 coupled to annular extension 426 adjacent flange 206 to a seal second end 264 axially spaced apart from flange 206. Seal element 205 also includes a through-passage 266 to receive a tubular member or string, an annular recess 468 extending from seal first end 262, and a radially outermost surface 212, which extends from first end 262 to second end 264. Annular extension 426 of insert 404 is disposed and held in annular recess 468, which is contoured to match this extension 426. For example, recess 468 is generally cylindrical and includes a radially-inward, annular indentation 469 to receive protrusion 431. As previously described, surface 212 includes a tapered first region 272 and a tapered second region 274 extending from region 272 to seal second end 264, and a plurality of axial slots 214.

FIG. 8 shows an FEA plot of stress induced within a resilient, annular seal element 305 of a packing element 300 (FIG. 6). The plot shows stress results for regions along a cross-section; even so, the results are representative of volumetric portions of seal element 305. As described previously, seal element 305 extends from a first end 362 to a second end 364 and includes a through-passage 266, an annular recess 268 extending inward from first end 362, and a radially outermost surface 312. Although not shown, the FEA includes boundary conditions that assume rigid flanged, annular insert 204 is located along the radially outer portion of first end 362 and within annular recess 268 as shown in FIG. 6. In the plot, a box end 20 of a drill pipe 22 is located within through-passage 266 of seal element 305 with a neck 24 of box end 20 axially aligned with the innermost end of recess 268. More specifically, the plot represents a situation in which drill pipe 22 is being pulled upward through seal element 305. In the plot, stress levels are normalized and labeled as previously explained with respect to FIG. 1. In the scenario of FIG. 8, a region of low stress SL1 in seal element 305 occurs throughout a majority of seal element 305. A region of elevated stress SL2 occurs around the innermost end of recess 268 and neck 24. Highest stress SL3 extends radially between the innermost end of recess 268 and the intersection of box end 20 and neck 24 but not spanning the entire distance therebetween, unlike the scenario of FIG. 1. Thus, the configuration of a packing element 300 with an annular insert 204, which includes a tapered or curved radially-inward facing surface 230 (FIG. 5), results in a smaller portion of its seal element 305 experiencing highest stress SL3 as compared to the seal element of a conventional packing element, which is analyzed in FIG. 1.

FIG. 9 shows an FEA plot of stress induced within a resilient, annular seal element 205 of a packing element 200 (FIG. 4). The plot shows stress results for regions along a cross-section; even so, the results are representative of volumetric portions of seal element 205. As described previously, seal element 205 extends from a first end 262 to a second end 264 and includes a through-passage 266, an annular recess 268 extending inward from first end 262, and a radially outermost surface 212. Although not shown, the FEA includes boundary conditions that assume a rigid flanged, annular insert of the packing element is located along the radially outer portion of first end 262 and within annular recess 268 as shown in FIG. 4. Annular recess 268 is cylindrical, having axially extending walls. In the plot, a box end 20 of a drill pipe 22 is located within a seal element 205 with neck 24 of box end 20 axially aligned with the innermost end of recess 268. The plot represents a situation in which drill pipe 22 is being pulled upward through seal element 205. In the plot, stress levels are normalized and labeled as previously explained with respect to FIG. 1. In the scenario of FIG. 9, a region of low stress SL1 in seal element 205 occurs throughout a majority of seal element 205. A region of elevated stress SL2 occurs around the innermost end of recess 268 and neck 24. Disposed between the innermost end of recess 268 and the intersection of box end 20 and neck 24, a region of highest stress SL3 extends radially inward from recess 268 and radially inward from the through-passage 266, but spanning only a relatively small portion of the entire distance therebetween, unlike the scenario of FIG. 1. The size of the regions of the seal element in FIG. 9 that experience the highest stress SL3 and the regions that experience elevated stress SL2 are both reduced as compared to the seal element of a conventional packing element analyzed in FIG. 1, and as compared to packing element 300 analyzed in FIG. 8. Thus, as shown in FIG. 9, packing element 200 includes an annular insert 204 having a tapered or curved radially-inward facing surface 230 (FIG. 5) and also includes a seal element 205 having a radially outermost surface 212, and this configuration is understood to be a reason that seal element 205 is subjected to lower stress when a box end 20 is in seal element 205 as compared to stress experience by a seal element of a conventional packing element and as compared to some other packing element embodiments disclosed herein.

Some embodiments of packing elements in accordance with principles described herein include an annular seal element having an outer surface region defined by a single axially-extending character, such as being entirely frustoconical or entirely cylindrical, as examples. Some of these embodiments include slots 214.

While exemplary embodiments have been shown and described, modifications thereof can be made by one of ordinary skill in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations, combinations, and modifications of the systems, apparatuses, and processes described herein are possible and are within the scope of the disclosure. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. The inclusion of any particular method step or operation within the written description or a figure does not necessarily mean that the particular step or operation is necessary to the method. The steps or operations of a method listed in the specification or the claims may be performed in any feasible order, except for those particular steps or operations, if any, for which a sequence is expressly stated. In some implementations two or more of the method steps or operations may be performed in parallel, rather than serially. 

What is claimed is:
 1. A pressure control device for sealing about a tubular string, comprising: a flange disposed about a central axis, the central axis disposed on an axial plane; an annular extension extending from the flange and having a radially-inward facing surface; and an annular seal element coupled to the annular extension, the seal member having a through-passage for receiving the tubular string and an annular recess in which the annular extension is disposed; wherein the radially-inward facing surface comprises a tapered region that is nonlinear in an axial cross-section formed on the axial plane.
 2. The pressure control device of claim 1 wherein the radially-inward facing surface flares outwardly, away from the through-passage as the radially-inward facing surface extends axially from flange.
 3. The pressure control device of claim 1 wherein the radially-inward facing surface includes a first end extending from the flange and a second end spaced from the first end, and wherein the second end is further from the central axis than the first end.
 4. The pressure control device of claim 3 wherein the radially-inward facing surface comprises a first region extending from the first end and a second region extending from the first region, and wherein the second region is continuously curved in an axial cross-section formed on the axial plane.
 5. The pressure control device of claim 4 wherein the second region has a constant radius in an axial cross-section formed on the axial plane.
 6. The pressure control device of claim 3 radially-inward facing surface comprises a first region extending from the first end and a second region extending from the first region, and wherein the second region, in the axial cross-section, has a radius that has a value selected from the range 0 to 30 inches.
 7. The pressure control device of claim 1 wherein the annular seal element comprises: a seal first end adjacent the flange; a seal second end axially spaced apart from the flange; and a radially outermost surface having first and second regions; wherein the first region extends from the seal first end; and wherein the second region extends from the seal second end toward the seal first end and is frustoconical.
 8. The pressure control device of claim 8 wherein on the radially outermost surface, the second region intersects the first region.
 9. The pressure control device of claim 1 wherein the radially-inward facing surface lacks a radially inward annular protrusion.
 10. A pressure control device for sealing about a tubular string, comprising: a central axis; an annular insert; and an annular seal element coupled to the annular insert, the annular seal element comprising: a seal first end disposed adjacent the annular insert; a seal second end axially spaced apart from the annular insert; a through-passage extending through the seal first and second ends for receiving the tubular string; and a radially outermost surface including a first region extending from the seal first end and a second region extending from the seal second end toward the first region; wherein the second region tapers as it extends in a direction away from the annular insert.
 11. The pressure control device of claim 10 wherein second region on the annular seal element intersects the first region.
 12. The pressure control device of claim 10 wherein the second region on the annular seal element is frustoconical.
 13. The pressure control device of claim 10 wherein the annular insert comprises: an annular flange disposed about the central axis; an annular extension extending from the flange; and a radially-inward facing surface extending along the annular extension; wherein the annular seal element includes an annular recess in which the annular extension is disposed, annular recess extending from the seal first end; and wherein radially-inward facing surface of the annular insert includes a tapered region that expands radially outwardly as it extends axially away from the flange.
 14. The pressure control device of claim 13 wherein the radially-inward facing surface further comprises a cylindrical region extending from the flange to the tapered region.
 15. A pressure control device for sealing about a tubular string, comprising: a central axis disposed on an axial plane; an annular insert comprising: a flange disposed about the central axis; an annular extension concentric with the flange and extending from the flange; and a radially-inward facing surface extending along the annular extension; and an annular seal element coupled to the annular extension, the annular seal element comprising: a seal first end disposed adjacent the flange; a seal second end axially spaced apart from the flange; a through-passage extending through the seal first and second ends for receiving the tubular string; an annular recess in which the annular extension is disposed, the annular recess extending from the seal first end; and a radially outermost surface including a first region extending from the seal first end and a second region extending from the seal second end toward the first region; wherein the radially-inward facing surface of the annular insert includes a tapered region that expands radially outwardly as it extends axially away from the flange.
 16. The pressure control device of claim 15 wherein the second region on the annular seal element intersects the first region.
 17. The pressure control device of claim 15 wherein the tapered region is continuously curved on the axial plane.
 18. The pressure control device of claim 17 wherein the tapered region of the annular insert has a constant radius on the axial plane.
 19. The pressure control device of claim 15 wherein the radially-inward facing surface of the annular insert comprises: a first end coupled to the flange, a second end spaced from the first end; and a cylindrical region extending from the first end; wherein the tapered region extends from the cylindrical region toward the second end.
 20. The pressure control device of claim 19 wherein the tapered region of the radially-inward facing surface intersects the second end at a fillet; and wherein on the axial plane, the tapered region intersects the fillet at a tangent line that is disposed at angle between 5 and 45 degrees, inclusive, with respect to the central axis. 